1. Field of the Invention
The present invention relates to a memory check unit that checks a memory (diagnoses whether the memory has a fault) included in a radar system. Moreover, the present invention is concerned with a radar system including the memory check unit.
2. Description of the Related Art
On-board millimeter-wave radar systems (refer to, for example, Patent Document 1) identify an object located in front of a vehicle, and detect the distance to the object and the relative velocity of the object. The results of the detection are employed in control of an inter-vehicle distance control unit or the like, whereby safety is ensured.
The millimeter-wave radar system modulates the frequency of a transmitted signal produced by a continuous-wave radar, irradiates the resultant signal to a place in front of a vehicle, and receives a signal reflected from a target. The millimeter-wave radar system then calculates the distance from the vehicle to the target and the velocity of the target on the basis of a beat between of the transmitted signal and the radar-received signal. During the calculation, a memory, for example, a random access memory (hereinafter an RAM) is used to store the beat frequencies.
RAM products have their qualities checked in the stage of manufacture and are thus screened in order to detect a defective part. After a RAM is included in a system, it may become defective due to time-sequential degradation or any other factor. As for a radar system, there is a demand for RAM check that can be executed even during operation of the radar system for the purpose of ensuring safety.
However, when the system is in operation, the RAM is accessed. Therefore, RAM check cannot be executed at any timing. Consequently, the RAM included in the system is checked at the time of starting up the system, in a maintenance mode, or on any other specific occasion but the RAM check is not executed while the system is in operation.
A fault diagnosis circuit capable of executing a RAM check even when a system is in operation has been proposed (Patent Document 2). The fault diagnosis circuit diagnoses a fault of a RAM on condition that the RAM is not accessed by the system.
(Patent Document 1) Japanese Patent No. 2594728
(Patent Document 2) Japanese Unexamined Patent Publication No. 2000-322330
However, Patent Document 2 does not clarify a criterion for verifying that a RAM is not accessed by a system.
Consequently, when a RAM check unit described in Patent Document 2 is merely included in a radar system, RAM check cannot be executed while the radar system is in operation.